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-   -   Moly cooling (http://talk.craftweb.com/showthread.php?t=7899)

Pete VanderLaan 08-04-2010 07:46 PM

I think it's the case that if you see no change in the temps after eight inches keeping the fuel constant, that should work both ways Eben and it becomes a zero gain or loss. After eight inches, you're just wasting insulation and getting no change in your performance. You could certainly prove it if you have enough insulation and you want to take the time to do the experiment. I spent quite a number of days on it.

And Ed, it's always good to see you out there.

Peter Bowles 08-04-2010 09:26 PM

so it would be perfectly appropriate to wrap copper pipes around the furnace at 8 inches of insulation but no more...

Jon Myers 08-05-2010 01:08 AM

Quote:

Originally Posted by Larry Cazes (Post 89969)
Eben, I agree in concept. How have you determined that 8" is optimum? Theoretical data or just by experience?

There is a program from RHI called Heat Flow.... pretty interesting

Rollin Karg 08-05-2010 04:17 AM

Quote:

Originally Posted by Jon Myers (Post 89962)
how much insulation do you run on the top of your furnace?

Six layers of one inch. On this one, it looks like it has become compressed and we probably should add some more.

Pete VanderLaan 08-05-2010 05:45 AM

Quote:

Originally Posted by Peter Bowles (Post 89977)
so it would be perfectly appropriate to wrap copper pipes around the furnace at 8 inches of insulation but no more...

*******************
The ghost of David Williams is rattling its chains.

Lawrence Ruskin 08-05-2010 08:23 AM

Actually the guy I was talking about was the guy that designed my last furnace.

He was the head designer for Inproheat, a company that makes equipment for heavy industry.

He said three bats of insulation of different density,the heaviest on the inside; it worked like a charm, you could give that furnace a little kiss on it's steel shell which I sure can't do to my Stadelmelter...

David Russell 08-05-2010 10:05 AM

dangerous temps
 
hello to all. i have a question for steve, rollin, pete and any of you other knowledgable "molly men", that has been in my mind for a while and this topic seems the place to ask.

All this cooling on the top of the elements is too keep from reaching what temperature range?

i have documented the temps( with a heat gun) on my unit in all various stages of operation, staying between 175f - 220f.

Where does the danger zone start temperature wise?

thanks everybody

Larry Cazes 08-05-2010 10:31 AM

Quote:

Originally Posted by Jon Myers (Post 89979)
There is a program from RHI called Heat Flow.... pretty interesting

I have built theoretical models similar to this in past lives. The devil is in the details. The experimental data from the members here is very interesting, though.

Pete VanderLaan 08-05-2010 10:40 AM

Cooling the element tops keeps the fiber from melting into nothing, it keeps the passage brick from melting into nothing, It keeps the 0000 wire insulation from vanishing and the porcelain clamp from turning to powder. Anything that hits those parts at 2300F or higher is going to eventually dine on it. The element makes it to 2800F.

Cooling the buss block in the transformer keeps the aluminum buss bar from melting and going down in to the coils where if it goes through the enamel coating on the copper windings, you will need a new transformer.

These furnaces require vigilant maintenance and they can be wonderful.

And yes the small Stadelman furnace is underinsulated. It also cost 1/4 of the larger units. It was not designed as a production furnace but rather for the weekend glassblower. Steve always made that clear.

Pete VanderLaan 08-05-2010 10:42 AM

Quote:

Originally Posted by Peter Bowles (Post 89977)
so it would be perfectly appropriate to wrap copper pipes around the furnace at 8 inches of insulation but no more...

**************
It would be interesting to try this if you put constant fuel input into the furnace and then stabilized it. Then add the pipes. See if the temp goes down. If it does then the laws of thermodynamics are speaking. If it stays the same, we have a new ballgame.

It would take days to do this by the way.

Steve Stadelman 08-05-2010 11:04 AM

400f is a bad point for the junction between the aluminum straps and the heater shanks.

Yes, the 75lb unit was designed for the hobbyist, smaller, lighter, easier to ship and with a smaller profile to fit into a tiny workspace.

Edward Skeels 08-05-2010 12:03 PM

back to what Eben posted.

You are not paying to heat the addtional insulation. The furnace is not working harder. The additional insulation is simply containing the heat that would have been lost to the atmosphere after the eighth inch.

Jeff. How does insulation switch properties and go from retarding heat loss to promoting it? or were you just kidding around?

I agree with Jon, the Heatransfer program at HWR is very helpful.

Jeff Thompson 08-05-2010 12:20 PM

The cheapest part of this whole scenario is buying extra boxes of fiber blanket and buying sheet metal. Electricity, on the other hand, is very expensive, and it's a recurring cost. Don't you think that if it was possible to save money on electricity (or fuel) by simply adding a bunch more fiber and sheet metal that all our furnaces would be triple the circumference they currently are? I sure would.

David Patchen 08-05-2010 01:18 PM

Isn't the question about which absorbs heat more readily after 8 inches--the air or more blanket?

Edward Skeels 08-05-2010 04:56 PM

Quote:

Originally Posted by David Patchen (Post 89993)
Isn't the question about which absorbs heat more readily after 8 inches--the air or more blanket?

the question is whatever you want it to be.

Thermal Conductivity
at 80F,
air is approx .174 BTU/Hr ft2 (F)/in
8# 2600f fiber blanket is listed at .29 BTU/Hr ft2 (F)/in

at 500F,

air is approx .275 BTU/Hr ft2 (F)/in
8# 2600f fiber blanket is listed at .51 BTU/Hr ft2 (F)/in

so it would appear that air is a better insulator

but,

with added thickness, additional fiber retains more heat than free air

assuming a hot face temperature of 2000f on a vertical wall:

with a material thickness of 3 inches kastolite 30 backed by 6 inches of 8# density 1" blanket,

307 BTU/Hr ft2 heat pass through

add 6 more inches of fiber and

162 BTU/Hr ft2 heat pass through

ceramic fiber is simply a low mass material that contains a lot of air. Lower mass is lower conductivity. Mizzou is above 150#/cu.ft and not much of an insulator. 8# blanket is, well, 8#/cu.ft. Fluffy material provides more air pockets. It's the air pockets that slow down the energy transfer. Sawdust or shredded newspaper insulates well, but kind of flammable.

resources:
Heatransfer application at hwr.com
http://www.matweb.com/tools/unitconverter.aspx
http://users.wpi.edu/~ierardi/PDF/air_k_plot.PDF

Edward Skeels 08-05-2010 06:00 PM

Quote:

Originally Posted by Jeff Thompson (Post 89991)
The cheapest part of this whole scenario is buying extra boxes of fiber blanket and buying sheet metal.

The cheapest part of building a furnace is doing the math before you spend money.

Quote:

Originally Posted by Jeff Thompson (Post 89991)
Don't you think that if it was possible to save money... by simply adding a bunch more fiber and sheet metal that all our furnaces would be triple the circumference they currently are?

It is possible to save money on energy with more insulation. Do you want a larger furnace? What would be the actual savings in dollar value. Could that amount be offset with better sales, production or design? Do the math.

I like Jordan's "think for yourself". I'll ask a blower why they are working in a particular way and they often reply with something along the lines "that's how I was shown" or "so and so said to do it that way". I've actually heard "I read it on the internet". Not much critical thought going on. I mean, those are all good starting points, but ideas should be tested, not simply trusted.

Maybe one hasn't wrapped ones furnace with more blanket because one is of the sheep. Monkey see, monkey do. (because one is of the monkey?) Maybe because one has determined is wasn't the most effective means to an end.

Thomas Chapman 08-05-2010 08:58 PM

It's amazing how many studios you go into and they are set up just the way they must have seen it at college: low bench, top loading oven with massive counterweights, open-air powdering, walk a mile to get to a marver, et cetera.

Edward Skeels 08-06-2010 12:49 PM

diminished returns
 
I'd used the Heatransfer program many times and always looked at the same two numbers: heat flux in btu/Hr/sq.ft and shell temp.

I never went a step further and applied the numbers to the total surface area.

I'd always made my 300# gas furnace the same size because of space limitations on one side of the hood. (54" O.D.)

I am Ed; sheep army of one.:sheep:

An increase of Fiber from 6 to 12 inches in roof and walls would save about a dollar a day at current natural gas prices.

The second increase to 18 inches thickness would save an additional 50 cents per day.

There are additional actual savings as the burner would be turned down at each thickness increment; less exhaust gasses up the stack.

I don't have the brains to figure that.

Pete VanderLaan 08-06-2010 02:28 PM

I could never see the increase in savings after eight inches using the method I used to determine diminishing returns on fuel savings. Maybe there was something wrong in my thinking, but the temperature just stopped going up after eight inches all the way around. This did not include the floor since I could no longer get at it. I do think the savings become marginal compared to the space lost to a bazillion cubic inches of fiber around the furnace, not to mention the difficulty in gathering out of what becomes a tunnel.

Edward Skeels 08-07-2010 04:04 PM

I agree

the "savings" according to the hwr app is only theoretical. heat loss around the door, flue adjustment or just the time the door is open during gathers can loose more heat than additional fiber can save.

there is a finite amount of heat that can be saved compared to the unlimited potential of better marketing, product design or production methods.

the shop I rent now has free unmetered electricity. it's nice to have but the total value has a limit. if I built a small furnace for fiddling around, it wouldn't be worth more than several hundred a month. it's nice to have in the winter when we turn on the 5kw overhead radiant heaters.

if I could come up with the perfect "pet rock" product, energy overhead would be a minor concern. marketing would be the big expense. and new sails.

Sky Campbell 08-07-2010 04:59 PM

Quote:

Originally Posted by Edward Skeels (Post 90049)
if I could come up with the perfect "pet rock" product, energy overhead would be a minor concern. marketing would be the big expense. and new sails.

Words of wisdom. So true.

Pete VanderLaan 08-07-2010 05:38 PM

Pet Rocks? remember Bibilos from Smyers? That trip down memory lane aside, Labor is still the killer cost, or was when we could afford to hire people.

Pete VanderLaan 09-02-2011 05:57 PM

I have moved this thread to antiques and classics


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